This invention relates to a method for detecting Helicobacter pylori in fecal specimens.
H. pylori is a bacterium that is found in the upper gastrointestinal tract of humans which has been implicated in gastroduodenal diseases such as peptic ulcers, gastritis and other maladies. The bacterium was originally classified as a Campylobacter and then reclassified as a Helicobacter based on more detailed information regarding its ultrastructure and fatty acid composition.
A number of different techniques, both invasive and noninvasive, have been used to detect H. pylori. The invasive techniques involve gastric biopsies and cultures. The noninvasive techniques include a urea breath test, in which the patient is given C-13 or C-14 labeled urea with a beverage, and the detection of H. pylori antibody in sera using antigens in enzyme-linked immunosorbent assays (ELISA). Examples of the latter techniques are found in U.S. Pat. No. 5,262,156 to Aleonohammad and European Patent Application 0 329 570 to Blaser.
Several major antigens have been identified and used in immunoassays in the detection of H. pylori antibodies. However, these assays have not exhibited the specificity and sensitivity that are desired in serodiagnosis. Newell, D. G., et al. Serodian. Immunother. Infec. Dis., 3:1-6 (1989). One problem with of these immunoassays is cross-reactivity. Studies of the dominant antigens in H. pylori, in particular, the putative flagellar protein, which has a molecular weight of 60 Da, have shown that some of these antigen are not specific to H. pylori and also found in other bacteria such as C. jeuni and C. coli. A second problem that has been encountered in designing immunoassays for H. pylori is strain variation. Substantial differences in the antigens has been observed in different strains of H. pylori. These problems preclude designing an assay around the use of a single antigen. They also rule out the use of monoclonal antibodies. One approach that has been taken to improving the specificity and selectivity of antibody immunoassays for H. pylori has been to use a mixture of antigens from different H. pylori strains which mixture is enriched with certain antigen fragments. One ELISA which detects H. pylori antibodies in a blood sera is commercially available from Meridian Diagnostics. This assay uses a bacterial whole cell lysate as the antigen.
There are certain disadvantages to using an ELISA which employs antigens to detect the presence of H. pylori antibodies. In particular, the antibody titer in human sera remains high for a prolonged time (in some cases as much as six months) after the infection has been treated. Consequently, a positive test using this ELISA does not necessarily mean that the patient is currently infected and requires treatment for H. pylori infection. When confronted with a positive ELISA, treating physicians often order a gastric biopsy to confirm the presence of the bacteria before initiating antibiotic therapy. Therefor, the antigen-based ELISA does not eliminate the need for the invasive procedure. By contrast, if an immunoassay could be designed for detecting H. pylori antigen instead of the antibody, the need to obtain gastric biopsies to confirm infection could be reduced significantly because the antigen generally can not be detected in a patient within days of its treatment. Thus, there is a need for an ELISA which detects H. pylori antigen and, more particularly, there is a need for an ELISA for detecting H. pylori directly from fecal specimens.
While ELISA's for detecting microorganisms such as C. difficile and adenovirus in fecal specimens are known, in studies of patients with gastric biopsies which are positive for H. pylori, the bacteria ordinarily can not be cultured and isolated from the fecal specimens. This and the problems of cross reactivity and strain variation raised serious doubts that an ELISA could be designed that would be specific for H. pylori and sensitive enough to reliably detect H. pylori antigen directly from a fecal specimen.